Physical Oceanography, Vol. 18, No. 5, 2008
THERMOHYDRODYNAMICS OF THE OCEAN
MODES OF LINEAR STATIONARY RESPONSE OF THE ATMOSPHERIC
BOUNDARY LAYER TO A COLD SURGE IN THE BLACK SEA
M. V. Shokurov and M. I. Soldatkina
To describe the phenomenon of cold surges in the Black Sea in winter, we study the problem of
atmospheric response to a local heat source on the surface in two simple formulations. In the
shallow-water model, the planetary boundary layer of the atmosphere is homogeneous with vari-
able upper bound. In the second model, the boundary layer has a constant thickness and its stra-
tification is homogeneous.
In the one-dimensional problem, for a constant wind blowing perpen-
dicularly to the sea coast, the atmospheric response is determined by a single dimensionless par-
ameter called the Froude number.
Depending on its value, there are two possible different modes
of the response.
Fr < 1
(subcritical mode) corresponds to gentle winds, strong stratifi-
cations, thick boundary layers, and high velocities of inertial gravitational waves.
1 (supercritical mode) corresponds to strong winds, weak stratifications, thin boundary layers,
and low wave velocities. In the two-dimensional problem for a round sea, there are four qualita-
tively different types of response depending on the combination of two dimensionless parame-
ters: the Froude number and the ratio of the radius of the sea to the radius of deformation.
At present, the operative numerical models of atmospheric circulation and combined climatic models of the
atmosphere–ocean system have low spatial resolutions of about 100–200
km. These resolutions make it impos-
sible to reconstruct mesoscale atmospheric phenomena with horizontal scales of
in the model. In re-
cent years, the mesoscale processes are studied fairly extensively. The urgency of these investigations is deter-
mined, in particular, by the fact that mesoscale phenomena affect the regional specific features of the weather
and climate. The mesoscale phenomena are formed under the influence of various factors and prove to be fairly
diverse. Among different mesoscale problems, one can mention the classical problems of the influence of the
coastal features and temperature contrast between the sea and dry land on the atmosphere.
In summer, the temperature contrast between the sea and dry land varies with diurnal periodicity and leads
to the formation of mesoscale breeze circulation: daytime sea breeze and nighttime land breeze. For the winter
season, we observe a different typical manifestation of temperature contrast formed as a result of penetration of
cold continental air to the warm sea surface (cold surge). Cold surges can be regarded as a typical synoptic phe-
nomenon for the winter season at middle and high latitudes. They are observed in the Atlantic Ocean over the
warm Gulf Stream, over the Great Lakes in North America, and over the Black, Caspian, and Mediterranean
Seas and in the Pacific Ocean. In the cold surge, a new marine boundary layer with intense surface heat and
moisture fluxes and strong convective turbulence begins to develop inside the continental boundary layer from
Marine Hydrophysical Institute, Ukrainian National Academy of Sciences, Sevastopol, Ukraine.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
3–22, September–October, 2008. Original article submitted March 26,
2007; revision submitted September 5, 2007.
0928-5105/08/1805–0237 © 2008 Springer Science+Business Media, Inc. 237